SOI contact structures
Disclosed are an arrangement and a production method for electrically connecting active semiconductor structures in or on a monocrystalline silicon layer (12) located on the front face (V) of silicon-on-insulator semiconductor wafers (SOI, 10) to the substrate (13). The electrical connection (20) is made through an insulator layer (11). A stack of layers (30 to 32, 70 to 72) is disposed above the connection piece (20) on the insulator layer (11).
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The present application is a U.S. National Stage of International Patent Application No. PCT/DE2004/000146 filed Jan. 30, 2004, and claims priority of German Patent Application No. 103 03 643.1 filed Jan. 30, 2003. Moreover, the disclosure of International Patent Application No. PCT/DE2004/000146 is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention relates to SOI structures (silicon on insulator), in which electrical connections are provided between device structures in the upper semiconductor layer insulated from the substrate and the semiconductor substrate, which connections are formed through the insulating layer to the upper semiconductor layer.
2. Discussion of Background Information
An SOI structure consists of a thin semiconductor layer, which is located on a thin oxide layer. The oxide layer is typically formed as a buried oxide (BOX) and is also provided on a semiconductor layer, i.e., generally a silicon layer, that is, the silicon substrate, which usually has a thickness of 300 μm to 800 μm. This substrate serves the purpose of handling the structure. The actual device functions are realized in the semiconductor layer near the surface, similar to usual CMOS processes performed on homogenous silicon wafers.
A significant difference with respect to standard CMOS processes resides in the fact that the devices are dielectrically separated from each other by trenches which extend down to the insulating layer. Hereby, a mutual electrical interaction of the devices is significantly reduced. This dielectric isolation renders the SOI technology also suitable for high voltage applications.
On one hand, it is advantageous when the devices are not coupled to each other via the substrate. Thus, certain non-desired substrate effects may be avoided, such as latch-up, significant reverse currents at elevated temperatures, increased parasitic capacitances at the source/bulk or drain/bulk-pn junctions.
On the other hand, it is advantageous when a substrate connection is provided, for instance, to allow to incorporate into the circuit certain active or passive structures formed in the substrate. In this way, devices may also be integrated that are formed by different techniques not corresponding to the SOI technology. In this case, an electric contact to the substrate would be advantageous. The back side metallization of the substrate, which would be useable for this purpose is, however, not a component of the SOI technology. The corresponding packages do not provide a back side contact and, frequently, the number of pins is not sufficient in the integrated circuits so as to allow a contact to the back side or to root out such a contact.
SUMMARY OF THE INVENTIONThe invention provides an electrical connection of SOI device structures within an active silicon layer to the substrate, while circumventing or avoiding a back side metallization of the substrate. Thereby, the degree of integration of circuits is to be increased. Also, devices not corresponding to the SOI technology are to be taken into consideration.
The solution of the present invention is described in the claims. Further embodiments of the invention are defined in the dependent claims. By way of example, according to the invention the insulating layer comprises through holes in areas lacking the monocrystalline semiconductor layer, said through holes extend to the substrate and are filled with metal. At least one layer stack, comprising at least two respective layers, is located on the insulating layer. The first layer represents a passivation layer having an opening above the area of the metal filling, above which the second metallization layer is located, that is connected to the metal filling and that provides the electric contact between the substrate and structures prepared on the wafer front side. By way of further example, according to the invention, the insulating layer comprises worked through portions in areas not covered by the monocrystalline semiconductor layer, and the worked through portions extend to the substrate and are filled with a metal. At least one layer sequence is formed on the insulating layer, and the layer sequence is comprised of two respective layers. From the layers, a first one is a passivation layer having an opening above the metal filling, above which is located a second layer as a metallization layer, which is conductively connected to the metal filling and which provides electrical contact or a conductive structure to the substrate so as to contact or conductively connect structures prepared on the front side with the substrate. By way of still further example, the invention includes etching a through hole into the insulating layer (oxide layer) down to the substrate at locations, which are not covered by the active semiconductor layer, forming a metal via by filling the through hole with a metal layer that is bordered by the insulating layer, forming a passivation layer that is worked through at the metal via, depositing a further metal layer and if necessary patterning the same within the area of the device structures, said metal layer providing the electric contact to the structures prepared on the front side in the active semiconductor layer, and forming a further passivation layer. By way of still further example, the invention includes forming at least one via opening in an insulating layer at locations that lack an active semiconductor layer, said via opening extending to the substrate, forming a metal via by filling the via opening with metal that is substantially bordered by said insulating layer, forming a first passivation layer at the metal via, which layer is worked through or intercepted, forming a metal layer on said passivation layer, and forming a further passivation layer on said metal layer.
In this way, a via thus provides a connection of active structures located on the front side to the substrate. The connection may be provided as a single or a multiple connection, such as in the claimed layer stack, so that different device groups on the front side may be individually connected to the substrate.
Also, a connection of device structures from the front side with doped regions in the substrate is contemplated.
Formed on the insulating layer of the SOI wafer is at least one layer sequence consisting of respective two layers.
From these layers, a first passivation layer having an opening is located above the metal filling, above which a second layer is located as a metallization layer that is conductively connected to the metal filing and that provides electrical contact, that is, a conductive structure, to the substrate so as to contact or conductively connect to the substrate structures that are prepared on the front side of the SOI.
A multiple repetition results in a sequence of a respective passivation layer having an opening above the area of the metal filling, and of a respective metallization layer located above the passivation layer within the area of the metal filling.
An electrical contact is established between the substrate and the structures that are prepared from the front side of the wafer, so that the stack comprises different conductive height layers of several alternating metal and passivation layers, wherein the height layers have a different spacing with respect to the insulating layer.
Exemplary embodiments explain and complete the invention, wherein identical reference numerals denote identical elements.
For a more detailed explanation of the invention,
In this way, the via provides a connection of the active structures on the front side to the substrate. The connection may be provided as a single or a multiple connection, as is the case in the stack shown in
With the reference numerals provided in
A contact is formed at the interfaces between the metal of the via and the substrate. This contact may represent an ohmic contact or a Schottky contact. Both types of contacts are of technological relevance and may be specifically implemented.
The contacting of the substrate according to
The via 19 in the form of, for instance, an etched throughhole, is filled with a metal material for forming a metal layer (or a metal plug), which is substantially flush with the insulating layer on the upper side and lower side or which lands on the substrate layer 13 at the lower side.
In this way, the via represents a connection of active structures 40, 50 on the upper side (front side V) of the SOI wafer to the substrate 13 that has a back side R.
This via may be formed as an individual one or as multiple vias, as is shown for the stack in
Doped regions, which are not explicitly shown, may be provided on the surface of the substrate in the via opening 19. If a doped region is not provided, a Schottky contact 13c is created, as is illustrated in
The layer sequence 30 to 32, i.e., interleaved therein the layers 70 to 72, will be explained below.
In one manufacturing method, the stack structure of the layers according to
At locations that are not covered by the active semiconductor layer 12, i.e., the trench 12a, the insulating layer is provided with the via opening 19, particularly by an etch process, wherein the via opening extends to the substrate 13. A plurality of openings may be etched substantially simultaneously in a spaced apart relationship.
A metal via 20 is formed by filling in the respective via opening 19. The metal via is substantially flush with the insulating layer.
Above the metal via 20 a worked through passivation layer 30 is deposited as a first passivation that has a lateral extension and that is formed on the insulator 11. In a further process step, a metal layer 70 is formed, which reaches through the opened passivation layer at the worked through portion and that electrically contacts the metal layer 20 in the via opening, as is shown at 70a. The contact area 20a exhibits a recess, which substantially corresponds to the shape or extension of the worked through portion extending through the passivation layer 30.
If necessary, the first metal layer 70 may be patterned so as to provide the electrical contact within the area of the device structures. This is illustrated by means of the lateral conductor 70a, originating from the first metallization 70, in
A further passivation layer 31 is formed on the metallization 70 and is also opened as is the case for the first passivation layer 30.
The described sequence of layer pairs formed of a passivation and a metallization may be repeated several times, for instance, the second passivation 31 and the second metallization 71. A third passivation 32 and a third metallization 72 may follow, as is illustrated in
The passivation is worked through within the area above the metallic via 20 in order to form a central or inner core of metallic material for the conductive connection even of the uppermost metallization layer 72 to the substrate 13, that is, to the ohmic or Schottky contact 13c.
In the lateral direction, the further away the passivation layers are spaced from the insulating layer 11, the more they are reduced. The stack tapers in the upward direction, as is evident from the section of
In
The various electric conductors are connected via the stacked metallization and from different levels so as to commonly electrically contact them with the substrate 13 by means of the via 19/20.
In a plan view, the described structures and, in particular, the stack structure 80, is not provided in a circular form in its outer extension but, instead, is preferably of rectangular or square shape.
A plurality of the described stack structures may be arranged within areas, which are not covered by the active semiconductor layer, and which correspond to the “trench” 12a.
Claims
1. Substrate contacts extending to the front side of silicon-on-insulator semiconductor wafers, which are comprised of a thin monocrystalline silicon layer located on a thin insulating layer, wherein this double layer is carried by a monocrystalline semiconductor substrate, and the insulating layer comprises at least one through hole in an area lacking the monocrystalline semiconductor layer, said at least one through hole extends to the substrate and is filled with metal as metal filling, and at least one layer stack is located on the insulating layer, comprised of two respective layers, wherein the first layer represents a passivation layer having an opening above the area of the metal filling, above which the second layer as a metallization layer is located, that is connected to the metal filling and that provides the electric contact between the substrate and active structures prepared on the wafer front side.
2. The substrate contacts extending to the front side according to claim 1, wherein the insulating layer is a silicon dioxide layer.
3. The substrate contacts extending to the front side according to claim 1, wherein the passivation layer is a silicon nitride layer.
4. The substrate contacts extending to the front side according to claim 3, wherein the substrate is comprised of a highly doped monocrystalline silicon wafer.
5. The substrate contacts extending to the front side according to claim 1 wherein the metal filling forms an ohmic contact with the substrate.
6. The substrate contacts extending to the front side according to any of claim 1, wherein the metal filling forms a Schottky contact with the substrate.
7. A silicon-on-insulator semiconductor wafer having at least one substrate contact extending to the front side, wherein said wafer has a patterned monocrystalline semiconductor layer located on an insulating layer wherein the layers are carried by a monocrystalline semiconductor substrate, wherein
- (i) the insulating layer comprises worked through portions in areas not covered by the monocrystalline semiconductor layer, said worked through portions extending to the substrate and being filled with a metal,
- (ii) at least one layer sequence is formed on said insulating layer, the layer sequence being comprised of two respective layers;
- (iii) from the layers a first one is a passivation layer having an opening above the metal filling, above which is located a second layer as a metallization layer, which is conductively connected to the metal filling and which provides electrical contact or a conductive structure to the substrate so as to contact or conductively connect structures (40, 50) prepared on the front side with the substrate.
8. The semiconductor wafer of claim 7, wherein the insulating layer is a silicon dioxide layer.
9. The semiconductor wafer of claim 7, wherein the passivation layer is one of a silicon nitride layer and a plasma nitride layer.
10. The semiconductor wafer of claim 9, wherein the substrate is comprised of highly doped monocrystalline silicon.
11. The semiconductor wafer according to claim 7, wherein the metal filling forms an ohmic contact with said substrate.
12. The semiconductor wafer according to claim 7, wherein the metal filling forms a Schottky contact with said substrate.
13. The semiconductor wafer of claim 7, wherein the layer sequence is provided at least two times as a stack.
14. The semiconductor wafer of claim 7, wherein the layer sequence is provided at least three times for forming a layer stack having a metallic vertical core.
15. The semiconductor wafer of claim 7, wherein a geometry of the perimeter of the layer sequence has a polygonal configuration.
16. The semiconductor wafer of claim 7, wherein the layers of a respective layer sequence are substantially planar.
17. Silicon-on-insulator wafer having substrate contacts extending to a front side of the silicon-on-insulator semiconductor wafer, comprising:
- a monocrystalline silicon layer located on an insulating layer to form a double layer carried by a monocrystalline semiconductor substrate,
- the insulating layer comprises at least one through hole in an area lacking the monocrystalline semiconductor layer;
- the at least one through hole extends to the substrate and is filled with a metal as a metal filling; and
- at least one layer stack, located on the insulating layer, comprises at least two further layers, in which a first layer of the at least two further layers represents a passivation layer having an opening above the metal filling, and in which a second layer of the at least two further layers comprises a metallization layer located above the first layer of the at least two further layers and connecting to the metal filling, to provide an electric contact between the substrate and structures prepared on the silicon-on-insulator wafer front side,
- wherein the substrate contacts extend to the front side, and
- wherein the metal filling forms at least one Schottky contact with the substrate.
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Type: Grant
Filed: Jan 30, 2004
Date of Patent: Feb 3, 2009
Patent Publication Number: 20060160339
Assignee: X-Fab Semiconductor Foundries AG (Erfurt)
Inventors: Steffen Richter (Apfelstaedt), Dirk Nuernbergk (Erfurt), Wolfgang Goettlich (Erfurt)
Primary Examiner: Laura M Menz
Attorney: Greenblum & Bernstein P.L.C.
Application Number: 10/543,896
International Classification: H01L 21/00 (20060101);